Machine for centerless grinding



Jan. 20", 1931. A. G. E. HULTGREN 1,789,403

MACHINE FOR CENTERLESS GRINDING Filed June 8, 1927 /7 G. lVu/fgre)? INVG TOR I Patented Jan. 20, 1931 UNITED STATES m1. GUSTAF EMANUEL HULTGREN, OF SODERFORS, SWEDEN MACHIIT E FOR CENTERLESS GRINDING Application filed June 8, 1927, Serial No. 197,443, and in Sweden February 24, 1926.

16 polygonal rollers.

Fig. 4 is a diagrammatic view of the invention illustrating the formation of a polygonal body having a greater number of faces than that of Figs. 3a and 3b.

30 Fig. 5 is a view similar to Fig. 2 showing a modification of the invention.

Fig. 6 shows a modification of the invention whereby bodies of tapering shape may be formed.

In so-called centerless grinding the object being ground is usually in contact with three bodies: the grinding wheel, a stationary guide and another rotating wheel. This wheel is often called the regulating wheel,

50 because it-regulates the speed of rotation of the object. In Fig. 1 is shown a common arrangement of the object being ground 1, the regulating wheel 2, the grinding wheel 3 and the stationary guide 4. The point of contact, of object 1, when viewed endwise with wheel 2 is not usually diametrically opposite to its point of contact with wheel 2 but displaced towards guide 4.

The aim of centerless grinding, as heretofore carried out is to shape the surface of the object into an accurate surface of rotation,

usuall a circular cylinder. This aim, however, as not always been achieved, inasmuch as the object, which is hereafter referred to as the roller, will sometimes assume in section, the shape of a rounded, regular polygon, usually-having an odd number of faces, e. g. 3, 5 or 7. In consequence, for accurate work, finishing in a separate operation, by lapping, has become necessary.

The cause of this deviation from the round shape does not appear to be fully understood, nor is any method known of preventing it. Generally, the formation of a regular'polygon in centerless grinding indicates, that the conditions are such as to permit the roller, although polygonal, to maintain continuous contact with thebodies 2, 3 and 4 in all positions-during its revolution. Thus the polygonal shape, once formed, will be preserved in rinding down.

f the number of bodies in contact with the roller were increased, say, to four, the tendency for and chance of the formation of a polygonal shape would be lessened considerably or disappear, but, since a circleis already defined by three points on its periphery, the position of the fourth body, in order to ensure steady contact with the surface of the roller, would have to be adjusted, while the roller is being ground down, with such accuracy that this method cannot be realized in practice.

The difliculty' described above is overcome according to the present invention, in its simplest form, by replacing the fixed guide 4 of Fig. 1 by the rocking or swinging guide 4 of Fig. 2. The rocking guide has, viewed endwise, two points of contact with the roller. The rocking axis, here shown as a knife-edge, is parallel to the axis of the roller. The two points of contact are on opposite sides of a plane through both axes, 2 is the regulating wheel, 3 the grinding wheel. It is clear that during grinding, the rocking guide 4 automatically assumes such a position that both contact edges touch the roller in all positions of the latter. Thus continuous contact at four points of the periphery of the roller is ensured. I

Grinding experiments on rollers, using the arrangement shown in Fig. 2, have. proved that, starting with round rollers, round or polygonal rollers may be obtained dependingupon conditions to be illustrated by the fol- 95 lowing example. In Figs. 3a and 3?) is shown a case that actually occurred, where a round roller in grinding was gradually transformed into hexagonal shape 'with rounded sides. The grinding wheel-Swas steadily fed to- W0 wards the wheel 2. During each revolution the roller 1 passed through a series of angular ositions the extremes of which are shown in Figs. 3a and 3?), all other positions being intermediate between those two. The guide 4 rocked back and forth thus preserving contact with the roller in all positions at both edges. In Fig. 3a three adjacent corners of the hexagon are shown touching the regulating wheel 2 and the two contact edges of guide 4 respectively, while one of its sides touches the grinding wheel. In Fig. 3?) conditions are reversed.

By accurate measurement was determined that, in order to produce the hexagonal shape the following condition must be approximately fulfilled:

where or, ,8, y and 8 are the center angles shown where m, n, p, and g are integral numbers and 0; is the number of sides of the resulting polygon.

As an example, a regular polygonal shape with 17 sides may be obtained by making 41:3 2y :8=74', 1 :84", 7:63, 5:137",

- ing wheel towards the regulating wheel, the

diameter of the roller decreases and the angles on, 5, and 8 slowly change their values,

until, at a given instance, a tendency for another polygon to form will develop. In the transition stage the roller will usually be accurately circular. That stage may, however, be diflicult to catch in practice.

A provision that has the advantage of permitting fairly wide variation in the diameter of the roller, consists in making on equal to 7,

in other words, in placing the rocking guide centrally between the contacts of the rollers with the two wheels. As already demonstrated, for any polygonal shape to form, one of the following equations should be satisfied where m and p are integral numbers. Obviously then, since (1 no olygon may be formed and the roller must ecome circular or, if already circular, must remain so, as long as 11 Experiments have confirmed this conclusion.

The degree of roundness attainable by using the method now described may be estimated by the following example. We assume an error of 1% in adjusting oz=y. Hence If, further, the angles B and 8 are of the same order of magnitude as a and y, it follows that:

=(1 '+%)=q /2) and 1V=50+50+50+50=200. A polygon having 200 sides may, therefore, form. Generally, the number of sides of the polygon possible will be inversely proportionate to the error of adjustment.

When this method is carried out in practice, it is found that an approximate adjustment only is needed to produce perfect roundness. This is no doubt due to the fact that when polygons with many sides only are possible, the grinding will continuously alter the relation between the angles to suit new polygons, in other words no particular polygon will have time enough to establish itself and perfect roundness results.

It is not necessary that the roller glides over both contact edges of the rocking guide. One or both of these edges may be substituted by rolls, either driven or idle, mounted on the guide. In order to drive and regulate the speed of rotation of the roller it is only necessary that one of the rolls or wheels pres- 3 ent, not counting the grinding wheel, is driven. In case a regulating wheel is mounted On the rocking device,'a stationary guide may take the place of the wheel 2 of Fig. 2. Also two rocking devices may be used. In some cases it may be of advantage to mountv one or two rocking guides on one or both limbs of a lar er rocking device as shown schematically in Fig. 5. -By thus increasing the number of effective contacts the chances for polygonal shape to form are further minimized. i

If the axis of the rocking member or guide and the axes of the grinding and regulating.

conical or pyramidal objects may be ground,

depending upon the adjustment of the contact angles. An axial support at the large end ofthe object is then added to receive the thrust.

For the knife-edge of the rocking guide 1 may be substituted two journals moving in hearings or a cylindrical bottom surface resting on a cylindr cal groove of larger radlus of curvature. In the latter case the rocking action is effected by rolling of the one cylindrical surface upon the other.

. The description given above applies when the object being ground is not moved axially in grinding. For continuous grinding of cylindrical or prismatic objects that are fed.

axially through the machine the devices deicribed may also be employed with the modifications continued by the inclined positions of the axes of the grinding and regulating wheels to each other.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a machine for centerless grinding of surfaces of revolution or regular polygonal surfaces, a grinding wheel and work supporting members, one of said members being c011- stituted by a rotating wheel, at least one of said members being mounted to freely rock on a rigid support, the axis of the work being substantially parallel to the axis of the rock- 'ing movement of the last mentioned member, the latter beingprovided at each side of a plane determined by the two axes mentioned with a work engaging surface.

2-. In a machine for centerless grinding of surfaces of revolution or regular polygonal surfaces, a grinding wheel and work supporting members, one of said members being constituted by a rotating wheel, at least one of said members being mounted to freely,rock on a rigid support, the axis of the work being substantially parallel to the axis of the rocking movement of the last mentioned member,

the latter being provided'at each side of a plane determined by the two axes mentioned with work engaging portions, said work engaging portions being constituted by rockable members movable about axes parallel to the first mentioned rocking axis.

3. In a machine for centerless grinding'of conical orregular pyramidal surfaces, a

grinding wheel and work supporting members, one of said members being constituted by a rotating wheel, at least one of said members being mounted to freely rock on a rigid support, the axis of the work substantially intersecting the axis of the rocking movement of the last mentioned member, the latter being provided at each side of a plane determined by the-two axes mentioned with a 'work engaging surface.

4. In a machine for centerless grinding of 5 surfaces of revolution, a grinding wheel and least one of said members being mounted to I freely rock on a stationary support, the axis of the work being situated in the same plane as the axis of the rocking movement of the last mentioned member, the latter being provided at each side of said plane determined by the two axes mentioned with a work engaging surface, the rocking member being so disposed in relation to the grinding wheel and the regulating wheel that the distance from one work engaging surface of said rocking member to the work engaging surface of the grinding wheel is substantially equal to the distance fromthe other work engag ing surface of the rocking member to the work engaging surface of the regulating wheel.

5. In a machine for centerless grinding of regular polygonal surfaces, a grinding wheel ing wheel that a polygonal piece of Work of the desired size and shape when suitably placed in the machine will engage simultaneously one of said two wheels and the two said work engaging surfaces of the rocking memher at each of three polygonal edges and the other of said wheels at one'of its polygonal sides.

In witness whereof, I have hereunto signed my name.

AXEL GUSTAF EMANUEL HULTGREN. 

